The present invention relates generally to well tools, and more particularly relates to shifter tools used to selectively engage and operatively manipulate movable sleeve type flow control devices installed in a subsurface flow conductor at spaced production zones in a well.
In order to increase well production capacity and efficiency, the borehole of a modern subsurface well is often extended both vertically and horizontally through spaced series of subsurface production fracture zones containing retrievable production fluid such as oil and/or natural gas. Wells of this type are conventionally referred to as "offset" wells and typically have a generally vertical initial borehole section extending downwardly from the surface, and a lower borehole end section which is angled relative to the initial borehole section and in some instances may be generally horizontally disposed or even turn slightly upwardly.
The offset borehole, as in the case of a generally straight borehole is conventionally lined with a concreted casing having longitudinally spaced side wall perforations aligned with the fracture zones. In some wells the concreted casing by itself defines a well flow conductor for upwardly flowing production fluid, received from one or more of the fracture zones, to the surface. In other wells the flow conductor portion is defined by metal production tubing coaxially disposed within the casing. Fracture zone fluid entering the production tubing is flowed upwardly therethrough.
To selectively initiate and terminate fluid flow into the conductor portion of a subsurface well from the spaced apart fracture zones therein it is common practice to install a sliding sleeve type flow control device in the well flow conductor at each fracture zone. When the concreted wellbore casing defines the fluid conductor portion of the well, the flow control devices are installed directly in the casing. When production tubing defines the flow conductor portion of the well, the flow control devices are installed in the production tubing in alignment with casing side wall perforations in turn aligned with the fracture zones.
As conventionally manufactured, the typical sliding sleeve type flow control device comprises a generally tubular body portion having side wall inlet openings formed therein, and a tubular flow control sleeve coaxially and slidably disposed within the body portion for axial movement relative thereto between a closed position in which the sleeve blocks the body inlet ports, and an open position in which the sleeve uncovers the ports to permit fluid to flow inwardly therethrough into the interior of the body and thus into the interior of the well flow conductor--i.e., the borehole casing or production tubing as the case may be. The sliding sleeves thus function as movable valve elements operable to selectively permit and preclude fluid inflow to their associated flow control device body portions.
Generally cylindrical shifter tools, coaxially lowered into the interior of the well flow conductor, are conventionally utilized to shift selected ones of the sliding sleeves from their closed positions to their open positions, or vice versa, to provide subsurface flow control in the well. Under conventional practice, to effect this sleeve shifting the interior side surfaces of the sleeves have formed therein longitudinally spaced series of annular, transverse notches, and the shifter tool removably carries thereon a key set which is one of a series of key sets provided for interchangeable use on the tool.
Each sleeve interior side surface notch set has a pattern different than the interior notch set patterns on all of the other sliding sleeves and is configured to receive and lockingly mate with the correspondingly notched exterior side surface profile of only one of the key sets. The particular key set removably carried by the shifter tool is resiliently biased, in a direction perpendicular to the longitudinal axis of the tool, toward a normal or "seeking" position in which the notched side profile area of the key set projects outwardly beyond the exterior side surface of the tool body.
As the tool is coaxially lowered through the well flow conductor, and through nonmating sleeves toward its intended mating sleeve target, the notch sets of the nonmating sleeves successively cam the key set inwardly from its seeking position as the key set passes through the sleeves, but do not lockingly mate with the key set. When the key set is brought into longitudinal alignment with the target mating sleeve notch set the key set pops outwardly into locking engagement with the complementarily configured notch set, thereby locking the key set to the target sleeve. The coil tubing, upon the lower end of which the tool is carried, can then be pushed or pulled as needed to shift the target sleeve from one of its open and closed positions to the other position thereof.
While this conventional approach to subsurface flow control of a spaced series of production zones appears at first glance to be a relatively simple and straightforward one, it has proven to present a well known variety of problems, limitations and disadvantages. For example, in instances where the sliding sleeve flow control devices are disposed in a horizontal wellbore run (or other sharply deviated wellbore section) a wellbore length limit is typically reached at which the coil tubing cannot be downwardly pushed with enough force to effect its sleeve shifting tasks without buckling the coil tubing. The axial compression strength of the coil tubing thus becomes an undesirable, and unavoidable, limiting factor in the overall usefulness of this conventional key set/sliding sleeve subsurface well flow control system.
Another substantial disadvantage built into this conventional system is that in addition to the fact that each key set interchangeably mountable on the shifter tool "fits" only one of the sliding sleeves in the spaced series thereof, each key set is also "directional" relative to its single lockably mating sleeve.
More specifically, each key set is removably mountable on the tool in either of two opposite orientations relative to the tool. In one of these two opposite mounting orientations the key set can only lockingly engage its target sleeve when the key set is moving in one direction through the target sleeve. Correspondingly, in its reversed mounting orientation the key set can only lockingly engage its target sleeve when the key set is moving in the opposite direction through the target sleeve.
Each key set, in a selected orientation thereof, is mounted on the tool using a frangible release structure such as a shear pin. After the key set has been locked to its target sleeve, and the coil tubing has been pushed or pulled as needed to shift the sleeve to one of its open or closed limit positions within the flow control device body, it is necessary to push or pull the coil tubing with an even greater force to break the shear pin in order to disengage the key set from the sleeve and thereby permit the tool to be retrieved. This additional stress on the coil tubing, of course, undesirably limits the length to which it can be extended into an offset portion of a wellbore.
The combination of the directionality of these conventional key sets and the their frangible connection to the shifter tool tends to make the manipulation of the sliding sleeve flow control devices a tedious, time consuming, and relatively expensive task. To illustrate the potential magnitude of this problem one has only to envision a spaced number of sliding sleeve type flow control devices, say twenty, several thousand feet below the surface, each of the devices being representatively in its closed position.
The task of opening each of these twenty flow control devices, and subsequently returning them to their originally closed positions, requires a total of eighty tool trips along the length of the well flow conductor--twenty down and twenty up to open the devices, and twenty down and twenty up to later close the devices. Moreover, each of the forty times the shifter tool is brought to the surface its key set must be changed out and the broken shear pins replaced.
Because of the necessity of forcibly moving the target sleeve to one of its open and closed limit positions to break the key set shear pins and permit disengagement of the key set from the sleeve notch set, it is impossible with the conventional subsurface flow control system described above to only partially open or close any of the flow control device body inflow openings to make adjustments to the fluid inflow rate from a particular production zone into the well flow conductor--the fluid inflow openings in each device must either be fully blocked or fully uncovered. This disadvantage also, as a practical matter, precludes the possibility of incorporating both inlet ports and outlet ejection orifices into any of the flow control devices. Additionally, since the shifting tool (in a given trip down the well flow conductor) can only open or close its target sleeve, logging or other well inspection equipment, such as video cameras, cannot be operatively mounted on the lower end of the tool for use in conjunction therewith.
It can be readily seen from the foregoing that a need exists for improvements in subsurface well flow control systems, and associated shifter tool apparatus, of the general type described above. It is accordingly an object of the present invention to provide such improvements.